Cargo tank cleaning - A Continuing Hazard

An explosion off Penang, Malaysia, on board an oil/chemical tanker that killed one and injured five other crew members has been attributed to crew carelessness, manifold piping complexity, and dilatory maintenance.

Due to the incompatibility of the two grades of cargoes being shipped, the port side and starboard side common manifolds were used for discharging nitric acid and acrylonitrile, respectively, in order to follow the segregation requirement.

On 17th April, 2016, the Hong Kong registered 12,395 dwt tanker, the ‘No.3 Heung-A Pioneer’, arrived at Port Kelang and discharged about 6,800 tonnes of nitric acid that had been loaded in six tanks, two on each side of the vessel.

Discharge took place through the port common manifold, with the elbow spools connecting the port tanks to the manifold. The spools remained in place after the cargo had been dispatched. The vessel sailed the same day for Penang, and on the next day unloaded one grade cargo of about 2,000 tonnes of acrylonitrile through the starboard common manifold, with elbow spool pieces used to connect the starboard individual manifolds.

During the unloading operation, the crew discovered that the shut-off valve on the port individual manifold from cargo tank No. 8 was leaking, and they reported it to the Chief Officer.

The tanker sailed in a ballast condition, on route for Singapore. Thirty minutes out, the Chief Officer held a 20 minute cargo oil tank cleaning safety meeting with deck crew.

During the preparation for the tank cleaning operation, an elbow spool piece was wrongly fitted from the port common manifold to the port tank No. 8 individual manifold. As a result, the acrylonitrile residue was able to creep through the leaking manifold shut-off valve of tank No. 8 to mix with the nitric acid residue in the port common manifold.

Around eight minutes after cleaning began, a violent explosion occurred at the port side common manifold at main deck level, injuring six crew members on deck. The tanker returned to Penang and the injured crew members were sent ashore for medical treatment. One of them was certified dead in the hospital on the same day.

Investigation

The investigation, conducted by the Marine Accident Investigation and Shipping Security Policy Branch of the Hong Kong Marine Department, reached the conclusion that the ship management company of the vessel should:-

a)    Inform all Masters, officers and crew of the fleet on the findings of this accident investigation;

b)    Issue safety instructions on handling leaking valves of cargo oil pipelines during operation;

c)     Provide on board familiarisation training to crew of the cargo manifold piping arrangement;

d)   Review the on board procedures for handling incompatible cargoes, taking the following aspects into consideration:

Ø full risk assessment should be conducted for the tank cleaning operation;

Ø particular caution should be highlighted when using the common manifold. The ‘line-up checklist’ should include the use of elbow spool pieces to avoid any violation of the segregation requirement;

Ø procedures should be developed such as

Ø using warning signs, chain lock/seal or barrier on the individual manifolds to prevent them from being wrongly connected to the common manifold which may contain incompatible cargo;

Ø cargo compatibility information should be readily available to all crew members for reference;

Ø crew members involved in the cargo tank cleaning operation should attend all relevant safety and tool box meetings.

Tanker owners and operators will also be sent a Hong Kong Merchant Shipping Information Notice to promulgate the lessons learnt from the accident.

Full investigation report may be read at,

https://www.mardep.gov.hk/en/publication/pdf/mai160418_f.pdf